Importance of Skincare
Human skin acting as protective barrier for human body is continuously under exposure of internal and external causes that affect its condition and functioning. The external causes are primarily environmental factors, such as ultraviolet (UV) irradiation, free radicals, pollution and dirt in the air, toxic and allergic compounds, and mechanical damage. Endogenous factors might be some genetic predisposition, immune and hormone disorder, stress and lack of sleep and internal aging process. Consequently, skin exposed to these conditions could undergo slow deterioration over time as the daily damaging effects could gradually accumulate and eventually lead to a series of skin disorders such as skin irritation, allergy, pigmentation, wrinkling and dryness.
Dietary complementation with the essential skin care products could improve skin conditions. These skin care products could be in the form of toner, lotion, cream, paste, peeling-off, powder, gel or sheet with active ingredients loaded that directly altered skin appearance. The active ingredients include but not limited to vitamins, minerals, essential fatty acids, peptides, polymers, antioxidants, organic acid, and plant extracts which possess the function of skin moisturization and hydration, anti-acne, anti-irritation whitening, and prevention of aging. The active ingredients could be single component or mixture of components. For example, active ingredients for hydration function such as hyaluronic acid, petroleum could form a protective layer on skin surface to preventing water loss as, while as some chemical compounds such as glycerol, natural moisturizing factors (NMF) is able to absorb water within the air and maintain the moisturization level of the skin. Some active ingredients such as vitamin C could stimulate the formation of collagen to prevent wrinkle formation, and inhibit the tyrosinase activity and melanine pigmentation formation to whitening the skin. Some active ingredients such as antioxidants could directly decrease the amount of reactive oxygen species (ROS) in skin cells thus thwart oxidative stress, thereby preventing aging phenomenon.
Skincare is also critical for sanitary products such as diapers and sanitary napkins. Minimal rewet is desirable for these products such that complications such as diaper rash can be minimized.
Skincare Using Membranes for Delivery of Active Ingredients to Skin
Generally speaking the skincare mask or skin care membrane or transdermal patch could be defined as a subject which can be applied on the surface of skin for benefiting skin appearance and improve the condition of skin. Depending on the location applied, the skincare mask could be but not limited to facial mask, eye mask, hand mask, lip mask and neck mask. The form of skincare masks could be but not limited to paste, powder, gel, membrane and sheet. Based on its moisturizing condition, skincare masks could be mainly divided into two types: (1) dry type that does not contain any water; and (2) pre-moistened type that is fully loaded with nutrient solutions and functional ingredients. The latter is the most common type which occupies the most shares of current market, whereas the former is not very popular probably because of the inconvenience for usage.
Typical pre-moistened skin masks are generally composed of sheet materials carrying the following components: water, active ingredients, preservatives, water-thickening agents, plant extracts, soothing components, pH balancers, stabilizers, and fragrance ingredients. Among all these components, only the active ingredients are the contents that directly interact with skin for enhancing skin appearance and improving skin conditions. The functions of all the other components are to maintain the quality and stability of the skin masks. For example, the function of preservatives is to inhibit the bacteria growth as the moistened condition is prone to the formation of bacteria colony. The water-thickening agent is to increase the viscosity of the solution within the skin mask so that the solution will not flow elsewhere and stay within the skin mask applied area. Plant extracts and fragrance ingredients were usually used to attract consumers with pleasant smell and the usage of natural ingredients. Soothing component is to reduce the feeling of irritation caused by the filtration of active ingredients into skin. PH balancer is to adjust the pH of pre-moistened skin mask for optimal skin use whereas stabilizer is to maintain the chemical stability of the components within skin masks.
Dry skin masks are usually in the form of powder or dry membranes or dry sheets. Dry skin masks do not contain any water. The usage of dry skin masks requires pre moisturization procedure. Dry skin masks do not contain preservatives, water-thickening agents, pH balancers, and stabilizers. Consequently dry skin masks significantly reduce the risk of skin allergic reaction, skin sensitive issues and some side effects caused by preservatives and other chemicals.
Delivery of active ingredients via transdermal path is primarily limited by skin's outermost layer called stratum corneum (SC), which is 10 to 20 μm thick. The SC layer is composed of non-living corneocyte cells with cross-lined keratin and a mixture of intercellular lipids forming a brick and mortar structure. Only small molecules and lipids can diffuse through the skin barrier and transport across the stratum corneum. The size of the molecule which is tied to its molecular weight is an important factor that determined its penetration efficiency. Most molecules are too large to make its way through the skin. According to the 500 Dalton rule for skin penetration of chemical compounds and drugs, anything smaller than 500 Daltons can penetrate skin whereas anything larger than 500 Daltons cannot. (Bos, Jan D., and Marcus MHM Meinardi. “The 500 Dalton rule for the skin penetration of chemical compounds and drugs.” Experimental dermatology 9.3 (2000): 165-169.)
Different Types of Membranes for Delivery of Active Ingredients to Skin
Typical sheet-materials for pre-moistened masks on the market are generally made of non-woven sheets. The materials of the non-woven sheets include but not limited to polypropylene (PP), polyethylene terephthalate (PET), cotton, plant pulp, lyocell fiber, tencel fiber, biocellulose, rayon/viscose, and natural silk. The cost of non-woven sheet is low and its mechanical strength is high, though its limitations include poor skin contact and low absorbency. Furthermore, the polymers could cause sensitive skin. Therefore, this type of materials gradually diminished from the market. Cotton still occupies a certain share of skin mask market probably because of its low possibility of causing skin allergic reactions. But their disadvantage is its poor skin contact. Lyocell (Tencel) fiber was produced from pulp fibers. Therefore, it shares the same cellulosic properties with cotton but it is more soft and absorbent than cotton probably because of its special manufacturing technique.
The concept of nanofiber as skin mask materials has been proposed for over 30 years. The nanostructure rendered its excellent skin contact property. Active ingredients could be easily co-electrospun into the fiber and no preservative is needed for the final dry product. Furthermore, the excellent skin contact further leads to superior penetration of active ingredients of the mask. Various patents based on nanofibers for cosmetic purpose have been filed in recent years. (Tojo, Takehiko, and Masataka Ishikawa. “Method for attaching nanofiber sheet.” U.S. Patent Application Publication No. US2011/0256397. Tojo, Takehiko, Masataka Ishikawa, and Yoshimi Yamashita. “Nanofiber sheet.” U.S. Pat. No. 8,642,172. 4 Feb. 2014. Tojo, Takehiko, and Masataka Ishikawa. “Nanofiber laminate sheet.” U.S. Patent Application Publication No. US2013/0122069. Golubovic-Liakopoulos, Nevenka, Bhavdeep Shah, and Erik Andersen. “Compositions and methods for the delivery of agents.” U.S. Pat. No. 9,233,080. 12 Jan. 2016. Kim, Chan. “Cosmetic sheet formed from nanofiber with controlled dissolution velocity and method of manufacturing the same.” U.S. Patent Application Publication No. US2015/0272855. Smith, D., et al. “Electrospun skin masks and uses thereof.” PCT Int. Appl Publication No. WO 2001026610 A1 (2001): 14. Kusukame, Haruka, Tomoki Masuda, and Masayo Shinoda. “Method of producing an adhesive sheet for skin, cosmetic method and adhesive sheet for skin.” U.S. Patent Application Publication No. US2015/0265030. Nishio, Toshihiko, et al. “Water-soluble electrospun sheet.” U.S. Patent Application Publication No. US2010/0254961. Glenn VILE, Iain Cameron HOSIE, Simon Vaughan FEASEY. Bioactive nanofibres WO 2013035072 A1. Bo-Kyung Choi, Ji-Hwa Lee. Mask pack WO 2013078094 A1. Tom Sekiguchi, Aiko Watanabe, Yu Watanabe. A cosmetic sheet WO 2014125407 A1. Chen, Fung-Jou, Lei Huang, and Jeffrey Lindsay. “Gradient nanofiber materials and methods for making same.” U.S. Patent Application Publication No. US2006/0094320.) The disclosure of any patent and non-patent literatures cited herein are incorporated by reference in their entirety.
The above patents disclosed active ingredient-loaded nanofibers or nanofiber composites consisting of both nanofibers and other types of membranes or sheets. The disclosed nanofibers could be water dissolvable or non-dissolvable or semi-dissolvable by combining different type of nanofibers. The details are described as follows:
(1) Water-Soluble Sheet
Nishio et al. disclosed a water-soluble electrospun sheet consisting of high-molecular base materials and functional ingredients. Kim et al. disclosed a cosmetic sheet comprising water-soluble nanofibers with controlled dissolution velocity. Glenn et al. disclosed a dissolvable web structure article comprising active ingredients. Choi et al. disclosed a mask pack including a non-woven fabric layer and a nanofiber layer comprising a hydrophilic polymer.
(2) Laminated Sheet
In this category, the skin mask is composed of several different laminated layers. For example, Tojo et al. disclosed a nanofiber sheet containing a water-soluble adhesive component, a water-insoluble nanofiber layer and a base layer.
(3) Water-Insoluble Composite
Golubovic-liakopoulos et al. disclosed a composite formed by different type of nanofibers containing hydrophobic nanofiber and hydrophilic nanofibers, which intertwined together to form one single layer for delivery of cosmetic active ingredients. Chen et al. disclosed gradient nanofiber composites comprising several different types of nanofibers. Kusukame et al. disclosed an adhesive sheet by attaching a water-absorptive support to a water-permeable film delivering functional ingredients.
Shortcomings of the Prior Art
However, none of these nanofiber patents disclosed the distinctive physical properties of nanofibers such as the structure of nanofibers, the mechanical strength and the release property. These properties strongly affect the performance of nanofibers for skincare application. Furthermore, the water dissolvable nanofiber skin mask does not solve the poor skin contact problem. Poor skin contact will further lead to poor penetration of ingredients due to limited contact points between the mask and skin. The handling property is another concern of water-insoluble nanofiber skin mask. The electrospun membrane is very thin. When applied to the pre-moistened skin, it is easy to be ruptured when stretched during the using procedure. Moreover, it is very hard for them to move along the skin surface for best position adjustment due to large friction force between skin and the mask. As a result, there exists a need for nanofiber skin mask with good handling property as well as excellent skin contact.